The present invention relates to an apparatus for recovering fresh water and an apparatus for concentrating liquid, to both of which is applied a film having an excellent performance in preventing the formation of stationary drops of dew.
In depopulated areas such as remote islands and secluded places in the mountains, it is very important to obtain and keep safe drinking water. In recent years, further, with the desertification of agricultural fields, the conversion of desert to agricultural land is an important issue in development as well as a population problem, and water supply is a great problem to be solved for accomplishing the conversion of desert to agricultural land.
When a large amount of seawater is desalted, there is used a large-scale plant which uses an ion-exchange method, a diaphragmatic osmosis method, a reverse osmosis method or a multi-flash method. These methods are effective for treating a large amount of seawater, while a vast amount of the cost is required for installing the plant, and a large amount of energy is also required for desalting seawater. Therefore, the cost for desalting seawater is high, and in most cases, it is difficult to install such a plant in a remote island or on a secluded place in the mountains in terms of plant cost and the supply of energy for the operation of the plant.
FIG. 5 is a schematic view of a known apparatus for recovering fresh water or concentrating liquid by means of solar energy, which apparatus is shown, for example, in a literature "Series of Books on Energy Science, No. 5, Natural Energy", pages 15-16, by Takuya Honma, et al., published May 5, 1980 by Kyoritsu Shuppan K.K. This apparatus has a roof member 10 made of glass or plastic, a base member 14, a liquid reservoir member 18 provided in the base member 14 and a liquid recovery member 16 provided in the base member 14.
In the above apparatus, sunlight which is transmitted through the roof member 10 increases the temperature inside the apparatus, and evaporates seawater stored in the liquid reservoir member 18. The evaporated water is condensed on the inner surface (to be sometimes referred to as "ceiling" hereinafter) of the roof member 10 due to a temperature difference between the roof member exposed to the atmosphere, and the ceiling, whereby distilled water is obtained.
However, the above apparatus has the following problem. Steam is condensed on the ceiling of the roof member 10, and the condensed water drops from the ceiling due to its own weight. That is, the water recovery ratio decreases or the liquid concentration efficiency decreases. There is another problem in that the condensed water on the ceiling of the roof member 10 prevents the transmission of sunlight.